Method of waterproofing the surface of a polymer work piece

ABSTRACT

The invention relates to a method of waterproofing the surface of a polymer work piece. The aim of the invention is to prevent liquid or gaseous, hydroxyl-group (OH group) containing substances, such as water, vapor or glycerol, from diffusing into a polymer surface. To this end, the work piece is treated with at least one organic solvent that blisters the surface of the polymer work piece, thereby diffusing at least one waterproofing agent dissolved in the solvent into the surface of the polymer work piece, said waterproofing agent being a silicon-organic compound. The solvent is allowed to react and is then removed from the polymer work piece, whereby at least a part of the waterproofing agent remains bound in the surface of the polymer work piece. The inventive method provides a means for treating, in one steep bath, polymer work pieces or work pieces with polymer surfaces of any shape and size and also polymer surfaces with cavities and bulges in a simple and cost-effective manner, requiring only small quantities of the waterproofing agent and extremely little time. The so treated polymer work piece can be used in areas of high temperature and/or regions with high ambient temperatures.

DESCRIPTION

[0001] The invention relates to a method for waterproofing the surfaceof a polymer workpiece.

[0002] Waterproofing makes it possible to prevent liquid or gaseoushydroxyl group (OH group)-containing substances, such as water, watervapor, or glycerin, from diffusing into a polymer surface.

[0003] It is know that the diffusion of liquids, such as water orglycerin, into the polymer surface is enhanced by a specific interactionbetween the functional groups of the polymer surface, e.g. carbonylgroups, and the hydroxyl groups of the liquid. Consequently, variousknown coating processes for modifying polymer surfaces aim to neutralizethe functional ester or carbonyl groups. For this purpose, the polymersurface is treated, for instance, by using an oxygen plasma so thatfunctional groups, such as OH groups, are formed on the polymer surface.Usually, the polymer surface is then chemically coated by a graftingreaction to prevent a specific interaction of the OH groups of theliquid with the carbonyl groups of the polymer surface.

[0004] In one method of this grafting technique, the chemical substanceprovided for the coating is added directly as a gas to the plasma and isthereby deposited on the polymer surface. This gas phase coating processmakes it possible, for instance, to form Teflon-like coatings on thepolymer surface by adding C₄F₈, or SiO-type coatings by addinghexamethyl disiloxane. In another method of the grafting technique, thechemical substance provided for the coating is mixed into a solution forwet application and is then applied to the polymer surface by means ofthis solution. This method is used, for instance, to produce a silanecoating on the polymer surface by treating the polymer surface with anoctadecyl trimethoxy silane/toluene solution. Both of these methods,however, can be used only at locations on the polymer surface where thefunctional OH groups were created, for instance by the oxygen plasmatreatment.

[0005] These coating methods presume corresponding ion or plasma sourcesand vacuum technology and thus involve substantial equipment complexityand costs. These methods are moreover time-consuming since the polymersurface to be simultaneously treated is limited to the diameter of theion beam. A further drawback of these methods is that they aredirection-dependent, i.e. good results are obtained only if the surfaceof the workpiece to be treated can be oriented nearly perpendicularly tothe ion or plasma beam. As a result, polymer surfaces with cavities andcurvatures as well as wall areas that are oriented parallel to the ionbeam cannot be adequately treated.

[0006] Thus, the object of the invention is to provide a method forwaterproofing the surface of a polymer workpiece, which is suitable alsoto treat polymer surfaces with cavities and curvatures in a simple andcost-effective manner.

[0007] The method for waterproofing the surface of a polymer workpieceis characterized by the following process steps:

[0008] a) the workpiece is treated with at least one organic solventthat swells the surface of the polymer workpiece and

[0009] b) at least one waterproofing substance, which is anorganosilicon compound dissolved in the solvent, diffuses into thesurface of the polymer workpiece, and

[0010] c) after a contact time, the solvent is removed from the polymerworkpiece, and at least a portion of the waterproofing substance remainsembedded in the surface of the polymer workpiece.

[0011] This method is used to waterproof the surface of a polymer workpiece by using an organic solvent to swell the polymer surface and toserve as a carrier for at least one waterproofing substance contained inthe solvent. This causes the waterproofing substance, which is anorganosilicon compound, to diffuse into the surface of the polymerworkpiece together with the solvent. After a contact time, the organicsolvent is removed from the polymer workpiece, while at least a portionof the waterproofing substance remains embedded in the surface of thepolymer work piece. This embedding advantageously takes place due to theinteraction of the waterproofing substance with the polymer chains inthe surface of the polymer work piece. To foster this embedding of thewaterproofing substance into the surface of the polymer material, theorganosilicon compound preferably has bulky organic groups, whichthrough steric interaction with the polymer chains prevent the embeddedwaterproofing substance from diffusing out of the surface of the polymermaterial. As a result, as well as due to the hydrolysis stability of theorganosilicon compound relative to water, a long-term effect of theinventive waterproofing of the surface of a polymer material isachieved. Furthermore, the treated polymer workpiece can be used inareas with elevated temperatures and/or regions with high outsidetemperatures.

[0012] The inventive embedding of a waterproofing substance, which is anorganosilicon compound, into the surface of the polymer workpiecereliably prevents the specific interaction between the hydroxyl groupsand the functional groups of the polymer matrix, e.g. carbonyl groups,and thus blocks access to the polymer matrix for liquid or gaseoushydroxyl group-containing substances, such as glycerin, water or watervapor.

[0013] The preferred treatment method of a polymer workpiece is toimmerse the polymer workpiece into a bath with an organic solvent thatcontains the inventive waterproofing substance. After a brief contacttime, during which the polymer surface swells due to the solvent and thewaterproofing substance diffuses into the polymer surface, the polymerworkpiece is removed from the bath. The polymer workpiece is then dried,which causes the solvent to evaporate out of the polymer matrix and atleast a portion of the waterproofing material to remain embedded betweenthe polymer chains in the polymer workpiece. Consequently, the inventivemethod for waterproofing the surface of a polymer workpiece can be usedto treat any polymer surfaces with cavities and curvatures. This methodis furthermore particularly simple and cost-effective and can be used atalmost any place since only a bath and small amounts of the inventivewaterproofing substance are required.

[0014] The publication by Katz et al., “Ultraviolet Protection ofTransparent PVC Sheets by Diffusion Coatings,” Proceedings of the A.C.S.Div. of Org. Coatings and Plastics, 36 (1), pp. 202-205 (1976) describesa diffusion or impregnation process of a UV absorbing material into aPVC workpiece to increase UV resistance. In this process, an organicsolvent is used as the carrier for the UV stabilizer. The PVC workpieceis swelled by means of the organic solvent and the UV stabilizer isthereby introduced into the polymer workpiece. After drying, the UVstabilizer remains in the polymer surface.

[0015] Variations of this method for introducing a UV stabilizer intothe polymer surface are known and are described in European PatentApplication EP 0 306 006 A2. The described methods disclose no hintsregarding either a method for waterproofing the surface of a polymerworkpiece or the inventive waterproofing substance, which is anorganosilicon compound.

[0016] Preferably the waterproofing substance is an organosiloxane, analkyl silyl fluoride, an aryl silyl fluoride, an alkyl aryl silylfluoride, or an alkoxy silyl fluoride.

[0017] According to a first embodiment, the organosilicon compound is anorganosiloxane. Organosiloxanes comprise both linear molecules of theformula R₃Si—[OSiR₂]_(n)—O—SiR₃ with n≧0, as well as cyclic molecules ofthe formula [OSiR₂]_(m) with m≧3, where R represents same or differentorganic groups. Preferably R is an alkyl group R′ or an aryl group R″,as specified in further detail below. An example of a linearorganosiloxane according to the first formula given above is1,1,3,3-tetraisopropyl disiloxane-1,3-diyl. An example of a cyclicorganosiloxane according to the second formula given above is octamethylcyclotetrasiloxane.

[0018] According to embodiments 2 to 5, the organosilicon compound is analkyl silyl fluoride, an aryl silyl fluoride, an alkyl aryl silylfluoride, or an alkoxysilyl fluoride.

[0019] Alkyl silyl fluorides according to the second embodiment comprisemolecules of the general formula R′_(n)SiF_(4-n) with n≧2, preferablyn=3, where R′ represents same or different alkyl groups. The preferredgroups R′ are specified in greater detail below. Examples of such alkylsilyl fluorides according to the above formula with preferred groups R′are (triisopropyl)silyl fluoride, di-tert-butyl silyl difluoride anddimethyl trityl silyl fluoride.

[0020] Aryl silyl fluorides according to the third embodiment comprisemolecules of the general formula R″_(n)SiF_(4-n), with n≧2, preferablyn=3, where R″ represents same or different aryl groups. Preferred arylgroups R″ are specified in greater detail below. Particularly preferredaryl silyl fluorides are diphenyl silyl difluoride and triphenyl silylfluoride (TPSF). A particular advantage of using TPSF is its goodsolubility in known solvents, which are used to swell the polymerworkpiece. This ensures high flexibility of the inventive method, sincethe surfaces of any polymer material can be treated by simply selectinga suitable solvent.

[0021] Alkyl aryl silyl fluorides according to the fourth embodimentcomprise molecules of the general formula R′_(n)R″_(m)SiF_(4-n-m) withn≧1, m≧1 and n+m≧2, preferably n+m=3, where R″ represents same ordifferent aryl groups and R′ same or different alkyl groups. Preferredgroups R′ and R″ are specified in greater detail below. Examples of suchalkyl aryl silyl fluorides according to the above formula with preferredgroups R′ and R″ are dimethyl phenyl silyl fluoride, diphenyl methylsilyl fluoride, tert-butyl diphenyl silyl fluoride, and(pentafluorophenyl) dimethyl fluoride.

[0022] Alkoxy silyl fluorides according to the fifth embodiment comprisemolecules of the general formula (RO)_(n)R_(m)SiF_(4-n-m) with n≧1, m≧0and n+m≧2, preferably n+m=3, where R stands for the same or differentaryl groups R″ or alkyl groups R′. Preferred groups are specified below.An example of a preferred alkoxysilyl fluoride is tert-butyl oxydiphenylsilyl fluoride.

[0023] It is also feasible according to the invention to use a mixtureof one or more organosilicon compounds, preferably according to theabove embodiments.

[0024] A preferred alkyl group R′ according to the above embodiments isa linear or branched alkyl group R′ with 1 to 4 C atoms, such as methyl,ethyl, n-propyl, i-propyl, n-butyl, i-butyl or tert-butyl. Particularlypreferably, one or more groups R′ are bulky groups, such as i-propyl,i-butyl or tert-butyl. To achieve bulkiness, one or more alkyl groups R′can also have bulky substituents, such as an aryl group. An example ofsuch a group R′ is triphenylmethyl-, which is also referred to astrityl-. To increase the waterproofing action, one or more alkyl groupsR′ are advantageously monosubstituted or multiply substituted withfluorine.

[0025] A preferred aryl group R″ according to the above embodiments is aphenyl group. To increase the waterproofing action, one or more arylgroups R″ are advantageously monosubstituted or multiply substitutedwith fluorine.

[0026] Preferably, the waterproofing substance is used in the solvent atconcentrations of between 1% by weight and 55% by weight.

[0027] In a first preferred variant of the invention, the waterproofingsubstance in the solvent is used at a concentration of between 1% byweight and 10% by weight. The use of such small amounts of thewaterproofing substance, e.g. triphenyl silyl fluoride, is preferredparticularly for the waterproofing of optical polymer surfaces, sincethis makes it possible to retain the optical quality of the surfaces,e.g. their reflection properties.

[0028] In a second preferred variant of the invention, the waterproofingsubstance in the solvent is used at a concentration of between 10% byweight and 55% by weight. With the use of these correspondingly largerpercentages of the waterproofing substance in the solvent, a layer witha particularly high content of the waterproofing substance forms in thepolymer surface. Furthermore, our own tests have shown that the use ofthe correspondingly large percentages of the waterproofing substance inthe solvent enables the formation of a layer of the waterproofingsubstance on the polymer surface. These tests have also shown that theformation of this layer on the polymer surface can be prevented if thepolymer workpiece is rinsed with a solvent, e.g. ethanol, isopropanol ortoluene, immediately after the inventive treatment.

[0029] Preferably, the workpiece is treated at a temperature of belowthe melting temperature of the waterproofing substance. The uppertemperature limit of the dipping bath must be selected below the glasstransition temperature of the polymer workpiece to be treated to ensurethe dimensional stability of the workpiece. The lower temperature limitof the dipping bath is determined, respectively, by the polymerworkpiece to be treated and by the selection of the solvent based on theswellability of the polymer workpiece.

[0030] Preferably, the workpiece is treated at a temperature rangingbetween 0° C. and 60° C. This makes it possible to use simple heatingdevices to heat the dipping bath. Since it is especially preferred tocarry out the treatment of the workpiece in the dipping bath at roomtemperature, i.e. between 10° C. and 30° C., it is even possible todispense with a corresponding heating device.

[0031] Preferably a mixture of at least two organic solvents is used. Atleast the first solvent should be capable of swelling the surface of thepolymer workpiece and at least the second solvent of dissolving thehydrophobic substance. This results in a wide range of possibleselections for both the first and the second solvent. The two solventsand their corresponding percentages by weight are selected as a functionof the polymer workpiece to be treated and the waterproofing substance.For instance, acetone is preferably used in small amounts to dissolvethe waterproofing agent, such as triphenyl silyl fluoride.

[0032] For the organic solvent, one or more solvents is preferablyselected from the group comprising the low-molecular (C₁-C₁₀) saturatedor unsaturated, linear, branched or cyclic, possibly substitutedalkanes, alcohols, ethers, esters, aldehydes, ketones, N,N-dialkylamides, aromatic compounds. Examples of the solvents of the above groupare hexane, heptane, octane, nonane, decane, decahydro naphthalene,methanol, ethanol, propanol, hexafluoropropanol, butanol, pentanol,hexanol, di-n-butyl ether, tert-butyl methyl ether, butyl acetate,tetrahydrofuran, methyl-, ethyl-, propyl-, butyl- or pentylacetate,acetone, hexafluoroacetone hydrates, methyl ethyl ketone, methylisobutyl ketone, cyclopentanone, cyclohexanone, N,N-dimethylformamide,N,N-dimethyl acetamide, toluene, or xylene. To swell the surface of thepolymer workpiece, preferably a polar solvent is used for polar polymersand preferably a solvent of low polarity for non-polar polymers.

[0033] Particularly preferred organic solvents are butyl acetate,acetone and/or toluene. In the first variant of the invention, the useof butyl acetate is preferred since this solvent readily dissolves theTPSF active substance and also ensures that the optical quality, e.g.reflection properties, of the surfaces is retained when, for instance,PMMA polymer surfaces are treated. The use of toluene is preferred forshort residence times of the polymer workpiece in the solvent.

[0034] Preferably, the polymer workpiece comprises a thermoplastic or anelastomer polymer material. Examples of such polymer materials made of athermoplastic material are polystyrene (PS), polypropylene (PP),polyethylene (PE), cyclo-olefine copolymer (COC), polymethylmethacrylate(PMMA), polycarbonate (PC), polyoxymethylene (POM), polysulfone (PSU),polyphenylene ether (PPE), polyetheretherketones (PEEK), polyether imide(PEI), polybutylene terephthalate (PBT), polyacrylate, self-reinforcingpartially crystalline polymers (LCP), polyethylene terephthalate (PET),polyvinylidene fluoride (PVDF), cyclo-olefin polymer (COP), polyvinylacetate, polyvinylidene chloride, a copolymer based on acrylonitrile,butadiene and styrene (ABS) or a copolymer based on acrylates andethylene. Examples of such polymer materials made of an elastomer arepolyurethane (PUR), polybutadiene (BR), ethylene propylene terpolymer(EPDM), nitrite rubbers (NBR), styrene butadiene rubber (SBR), andnatural rubber (NR).

[0035] Preferably, the polymer workpiece is treated with a contact timeof less than 2 hours, preferably less than ½ hour. Thus the inventivewaterproofing of the surface of a polymer workpiece requires very littletime.

[0036] Preferably, the waterproofing substance remains in the surface ofthe polymer workpiece to a penetration depth of less than 50 μm,particularly less than 20 μm. This shallow penetration depth of thewaterproofing substance, e.g. TPSF active substance, into the surface ofthe polymer workpiece prevents mechanical deformation and stresses inthe polymer workpiece and thus the formation of cracks along the polymersurface.

[0037] Preferably, the solvent is removed by applying a vacuum to thepolymer workpiece and/or by heating the polymer workpiece.

[0038] Removal of the solvent by applying a vacuum to the polymerworkpiece is particularly preferred in polymer workpieces with cavities,since this requires little time to remove the solvent from the cavities.

[0039] In polymer workpieces with curvatures, smooth surfaces and/orcavities that are directly accessible from the surface, the solvent ispreferably removed from the polymer workpiece by heating or drying. Thepreferred drying temperature ranges from 10° C. to 60° C. This preventsthe waterproofing substance from diffusing out of the polymer surface.It also makes it possible to use simple and inexpensive dryingequipment. Especially preferred is the use of room temperature(approximately 10° C. to 30° C.) for drying, since this eliminates theneed for drying equipment. In the case of the first preferred variant ofthe invention and the use of low percentages of the waterproofingsubstance, the treated polymer workpiece is preferably dried at roomtemperature. In general, the polymer workpiece can be used for itsintended purpose directly after removal of the solvent from the polymersurface.

[0040] A particular advantage of the invention is that the inventivewaterproofing makes it possible to treat surfaces of a polymer workpieceand workpieces with polymer surfaces of any shape and size. This makesit possible to prevent diffusion of liquid or gaseous hydroxylgroup-containing substances, e.g. water, water vapor or glycerin,including, e.g., in any component housings made of a polymer material ofoptical, mechanical, electronic or other components, with little timebeing required and at low costs.

[0041] Additional aims, advantages, features and possible applicationsof the present invention result from the following description ofseveral exemplary embodiments with reference to the drawings. All thedescribed and/or depicted features are the subject of the inventioneither per se or in any meaningful combination, irrespective of theirsummarization in the claims or the referencing.

[0042] In the drawings:

[0043]FIGS. 1a-c illustrates an inventive treatment of a polymerworkpiece in a dipping bath comprising a solvent and the waterproofingsubstance contained therein.

[0044]FIG. 2a is a comparison of FTIR absorption spectra of an untreatedreference sample of a polymer workpiece and a reference sample that wasstored in water and two comparison samples that were previously treatedaccording to the invention.

[0045]FIG. 2b is a comparison of the FTIR absorption spectra of anuntreated reference sample of a polymer work piece and a referencesample stored in glycerin and two comparison samples that werepreviously treated according to the invention.

[0046]FIG. 3 is a comparison of the absorption of water vapor of areference sample of a polymer workpiece as a function of time and threecomparison samples that were previously treated according to theinvention, in which the concentration of the waterproofing substance wasvaried.

[0047]FIGS. 1a to 1 c show an inventive treatment for waterproofing apolymer workpiece 1 in a vessel 7 filled with a dipping bath 2 toprevent diffusion of liquid or gaseous hydroxyl group-containingsubstances, e.g. water, water vapor or glycerin, from penetrating intothe surface 5, 6 of a polymer workpiece 1.

[0048] Test 1:

[0049] In a first exemplary embodiment of the invention, the inventivewaterproofing of a polymer workpiece 1 was tested for protection againstwater. For this purpose, an untreated PMMA workpiece 1 (GS typePlexiglas by Röhm) was divided into four test samples. One of these testsamples was subsequently used as an untreated first PMMA referencesample and a second test sample was stored in distilled water for twomonths and subsequently used as the second PMMA reference sample. Theother two test samples were used as the first and second comparisonsample and for this purpose were treated by means of the inventiveprocess after they were divided. According to FIG. 1, the two PMMAcomparison samples were immersed for 20 minutes at room temperature inan inventive dipping bath 2 consisting of butyl acetate 3 and 3% byweight of triphenyl silyl fluoride (TPSF) 4 dissolved therein. The butylacetate 3 caused the polymer surfaces 5 to swell. Consequently, thebutyl acetate 3 as the carrier and the TPSF active substance 4 dissolvedtherein can diffuse into a layer 6 of the polymer surface 5 as shown inFIG 1 b. Thereafter, the two comparison samples were removed from thedipping bath 2 and air-dried at room temperature. According to FIG 1 c,this drying process causes the butyl acetate 3 to escape from layer 6 ofthe polymer surface 5 and at least a portion of the TPSF activesubstance 4 to remain embedded in layer 6 of polymer surface 5. Thisconcludes the inventive treatment for waterproofing the surface 5, 6 ofthe polymer workpiece 1 and the polymer workpiece 1 can be used for itsintended purpose.

[0050] Subsequently, the first PMMA comparison sample was also stored indistilled water for two months. For experimental proof of the inventivewaterproofing of the polymer surface 5 of PMMA workpiece 1,approximately 50 μm thick layers each were removed from the two PMMAreference samples and the two PMMA comparison samples and examined bymeans of infrared absorption spectroscopy as shown in FIG. 2a.

[0051] The comparison of the FTIR absorption spectra of the referencesamples and the comparison samples makes it possible to show thespecific interaction between the functional carbonyl groups of thepolymer surface 5 and the liquid or gaseous hydroxyl group-containingsubstances, e.g. glycerin, water or water vapor, which may have diffusedinto the polymer surface 5. If these substances have diffused into thepolymer workpiece 1 of a comparison sample and a specific interactionbetween the functional carbonyl groups of the polymer material and thehydroxyl groups of the diffused substance has taken place, theassociated FTIR absorption spectrum shows a shift of both thecharacteristic absorption bands of the carbonyl groups, the so-calledcarbonyl peak, e.g. at a wave number of 1731.8 cm⁻¹ in PMMA and thecharacteristic absorption bands of the hydroxyl groups in water orglycerin.

[0052]FIG. 2a shows a comparison of the carbonyl peak of the four FTIRabsorption spectra taken with an infrared absorption spectrometer(Nicolet MAGNA 850) through a microscope (Nicolet NIC PLAN) of the firstuntreated PMMA reference sample (curve 8), the second PMMA referencesample stored in water (curve 9), the first PMMA comparison sampletreated according to the invention and stored in water (curve 10), andthe second PMMA comparison sample treated according to the invention(curve 11) without water contact of the PMMA workpiece 1.

[0053] According to FIG. 2a, curve 9 of the second PMMA reference samplewith water contact compared to curve 8 of the untreated first PMMAreference sample shows a widening and a shift of the carbonyl peaktoward shorter wave numbers. This widening and shift can be attributedto a specific interaction between the functional carbonyl groups of thepolymer surface 5 of the second PMMA reference sample and the hydroxylgroups of the water that have diffused into the polymer surface 5. Incontrast, the comparison of the corresponding carbonyl peak of curve 11of the second PMMA comparison sample without water contact and curve 10of the first PMMA comparison sample with water contact shows that bothcurves are nearly identical with curve 8 of the first untreated PMMAreference sample and are thus clearly distinct from curve 9 of thesecond PMMA reference sample with water contact. This shows that theinventive treatment of the PMMA workpiece 1 according to the two PMMAcomparison samples prevents diffusion of water into the surface 5, 6 ofthe PMMA workpiece 1. This is the first experimental evidence of theinventive waterproofing of the polymer surface 5 of a PMMA polymerworkpiece 1.

[0054] Test 2:

[0055] In a second exemplary embodiment of the invention, the inventivewaterproofing of a PMMA polymer workpiece 1 was tested for protectionagainst glycerin. For this purpose, the experimental procedure used intest 1 was repeated, except that the second PMMA reference sample andthe first PMMA comparison sample were stored in glycerin for two months.

[0056]FIG. 2b shows a comparison of the carbonyl peak of the four FTIRabsorption spectra taken with the infrared absorption spectrometer(Nicolet MAGNA 850) through a microscope (Nicolet NIC PLAN) of the firstuntreated PMMA reference sample (curve 12), the second PMMA referencesample stored in glycerin (curve 13), the first PMMA comparison sampletreated according to the invention and stored in glycerin (curve 14),and the second PMMA comparison sample treated according to the invention(curve 15) without glycerin contact of the PMMA workpiece 1.

[0057] A comparison of curve 13 of the second PMMA reference sample withglycerin contact and curve 12 of the untreated first PMMA referencesample shows a shift of the carbonyl peak toward the shorter wavenumbers. This shift can be attributed to a specific interaction betweenthe functional carbonyl groups of the polymer surface 5 of the secondPMMA reference sample and the hydroxyl groups of the glycerin that havediffused into the polymer surface 5 of the second PMMA reference sample.In contrast, a comparison of curve 14 of the first comparison samplewith glycerin contact and curve 15 of the second comparison samplewithout glycerin contact shows that both curves 14, 15 are nearlyidentical and, in distinction to the two curves 12, 13 of the tworeference samples, are measured without a shift of the carbonyl peaktoward shorter wave numbers. This demonstrates that the inventivetreatment of the PMMA workpiece I according to the two PMMA comparisonsamples prevents diffusion of glycerin into the surface 5, 6 of the PMMAworkpiece 1. This is the second experimental evidence of the inventivewaterproofing of the polymer surface 5 of a polymer workpiece 1.

[0058] Test 3:

[0059] In a third exemplary embodiment of the invention, the inventivewaterproofing of a PMMA polymer workpiece 1 was tested for protectionagainst water vapors. For this purpose, an untreated PMMA workpiece 1(Röhm GS Plexiglas) was first divided into four samples. These PMMAsamples were then weighed on a balance having an accuracy of ±0.1 mg.The average weight of the four samples was determined to beapproximately 0.7 g. One of the PMMA samples was subsequently used asthe untreated PMMA reference sample. The other three PMMA samples weresubsequently used as PMMA comparison samples and for this purpose weretreated in an inventive dipping bath 2 according to FIG. 1 for 20minutes at room temperature. The first PMMA comparison sample wastreated according to the invention in toluene with a TPSF concentrationof 12% by weight, the second PMMA comparison sample in toluene with aTPSF concentration of 23% by weight and the third PMMA comparison samplein butyl acetate with a TPSF concentration of 32% by weight. Thereafter,the three PMMA comparison samples were removed from dipping bath 2 andair-dried at room temperature. Subsequently, the second and third PMMAcomparison samples were rinsed under running toluene. Such anafter-treatment with toluene prevents the formation of a TPSF layer onthe surface 5 of the associated PMMA comparison sample. Subsequently,the reference sample and the comparison samples were placed into aclimatic chamber at a temperature of 60° C. and 90% air humidity forapproximately 5 days. Finally, the PMMA reference sample and the threePMMA comparison samples were weighed regularly during the duration ofthe experiment to determine the water absorption into the correspondingpolymer surface 5 of the associated PMMA workpiece 1.

[0060]FIG. 3 shows a comparison of the change in weight as a function oftime due to water or water vapor absorption of the PMMA reference sample(curve 16) and the first comparison sample (curve 17), the secondcomparison sample (curve 18) and the third comparison sample (curve 19),which were treated according to the invention. The comparison of curve16 of the PMMA reference sample and curve 17 of the first PMMAcomparison sample shows that the water absorption rate is nearlyidentical in the range of the first 10 hours. Thereafter, the two curves16 and 17 show that the inventive treatment of the first PMMA comparisonsample with TPSF concentrations of 12% by weight in toluene is capableof reducing the absolute amount of water absorbed in the range of thefirst 60 hours compared to the untreated PMMA reference sample.

[0061] A comparison of curve 18 of the second PMMA comparison curve andthe two curves 16 and 17 shows that the treatment of the second PMMAcomparison sample with a higher TPSF concentration of 23% by weight intoluene clearly reduces the amount of water absorbed. The comparison ofcurve 18 and curve 17 shows that the treatment of the second PMMAcomparison sample with a higher TPSF concentration makes it possible toreduce the absolute amount of water absorbed up to approximately 50hours after the inventive treatment of the PMMA comparison sample andthat subsequently the absolute amount of water absorbed is almost equal.A comparison of curve 18 of the second PMMA comparison sample and curve16 of the PMMA reference sample shows that the inventive treatment ofthe second PMMA comparison sample clearly reduces the absolute amount ofwater absorbed up to approximately 70 hours after the inventivetreatment of the PMMA comparison sample.

[0062] A comparison of curve 19 of the third PMMA comparison sample andcurves 16 to 18 shows that a further increase in the TPSF concentrationto 32% by weight dissolved in butyl acetate clearly reduces both thewater absorption rate and the amount of water absorbed over the entiretest duration of approximately 5 days.

[0063] The results of the use of the TPSF active substance dissolved inbutyl acetate in the experiment according to Test 1 compared with theexperiment according to Test 2 show that the use of small TPSFpercentages of less than 10% by weight is sufficient to prevent liquidhydroxyl group-containing substances, e.g. water or glycerin, fromdiffusing into the polymer surface 5. A further comparison with theexperiment according to Test 3 shows that to prevent gaseous hydroxylgroup-containing substances, e.g. water vapor, from diffusing into thepolymer surface 5 and/or at elevated temperatures, the use of higherTPSF percentages, e.g. 32% by weight, enhances the waterproofing of PMMAworkpieces 1.

REFERENCE NUMERALS

[0064]1 polymer workpiece

[0065]2 dipping bath

[0066]3 solvent

[0067]4 waterproofing substance

[0068]5 polymer surface

[0069]6 layer

[0070]7 dipping vessel

[0071]8-19 curve

1. Method for waterproofing the surface of a polymer workpiece (1) inwhich d) the workpiece is treated with at least one organic solvent (3)that swells the surface (5, 6) of the polymer workpiece (1), and e) atleast one waterproofing substance (4), which is an organosiliconcompound and is dissolved in the solvent diffuses into the surface (5,6) of the polymer workpiece (1), and f) after a contact time, thesolvent is removed from the polymer workpiece, while at least a portionof the waterproofing substance (4) remains embedded in the surface (5,6) of the polymer workpiece (1).
 2. Method as claimed in claim 1,characterized in that the waterproofing substance (4) used is anorganosiloxane, an alkyl silyl fluoride, an aryl silyl fluoride, analkyl aryl silyl fluoride, or an alkoxy silyl fluoride.
 3. Method asclaimed in claim 1 or 2, characterized in that the waterproofingsubstance (4) is used in the solvent (3) at a concentration of between1% by weight and 55% by weight.
 4. Method as claimed in claim 3,characterized in that the waterproofing substance (4) is used in thesolvent (3) at a concentration of between 1% by weight and 10% byweight.
 5. Method as claimed in claim 3, characterized in that thewaterproofing substance (4) is used in the solvent (3) at aconcentration of between 10% by weight and 55% by weight.
 6. Method asclaimed in any one of claims 1 to 5, characterized in that the workpieceis treated at a temperature of below the melting temperature of thehydrophobic substance (4).
 7. Method as claimed in any one of claims 1to 6, characterized in that the workpiece is treated at a temperature ofbetween 0° C. and 60° C.
 8. Method as claimed in any one of claims 1 to7, characterized by the use of a mixture comprising at least two organicsolvents (3), of which at least the first solvent is capable of swellingthe surface (5, 6) of the polymer workpiece (1) and at least the secondsolvent is capable of dissolving the waterproofing substance.
 9. Methodas claimed in any one of claims 1 to 8, characterized by the use of anorganic solvent (3) comprising one or more solvents selected from thegroup consisting of the low-molecular (C₁-C₁₀) saturated or unsaturated,linear, branched or cyclic, possibly substituted alkanes, alcohols,ethers, esters, aldehydes, ketones, N,N-dialkyl amides, aromaticcompounds
 10. Method as claimed in any one of claims 1 to 9,characterized in that the polymer workpiece (1) comprises athermoplastic or elastomeric polymer material.
 11. Method as claimed inany one of claims 1 to 10, characterized in that the polymer workpiece(1) is treated for a contact time of less than 2 hours, preferably lessthan ½ hour.
 12. Method as claimed in any one of claims 1 to 11,characterized in that the waterproofing substance (4) remains in thesurface (5, 6) of the polymer workpiece (1) at a penetration depth ofless than 50 μm, particularly less than 20 μm.
 13. Method as claimed inany one of claims 1 to 12, characterized in that the solvent (3) isremoved by applying a vacuum to the polymer workpiece (1) and/or byheating the polymer workpiece.